Regulations promulgated by various agencies of the United States government, as well as worldwide general endeavors, are directed to reducing the consumption of fuel, thereby compelling automobile manufactures to effect drastic reductions in the weight of motor vehicles. As a consequence, solid structures are no longer used in such specialized fields of use.
Instead, door-reinforced tubes have been substituted to secure the passenger space of a passenger car by stiffening the door structure and absorbing deformation work during an impact or collision. In other words, such tubes absorb the energy of impact (up to a point) and dissipate such energy by deforming, thereby preventing the door or other structure from buckling and injuring the passenger.
For example, in Federal Republic of Germany No. 3,621,697, stiffening grids are arranged within a hollow tubular section in a honeycomb, lenticular, square, or round cross-sectional profile. Such a configuration reduces the weight of the structure while simultaneously assuring a high degree of safety. However, reinforced tubes having stiffening grids arranged therewithin in the particular orientations shown in the prior art are disadvantageous in that during impact, when forces are exerted perpendicular to the longitudinal axis of the reinforcement tube, different opposing forces are produced depending upon the orientation of the tube. Consequently, such a door-reinforcement tube will take up different deformation work in different directions, and in other directions will buckle. Yet an additional disadvantage of such a tube, beyond the non-uniformity in deformation work, results from the great expense involved in both the manufacture and installation of the stiffening grids within the tubes in the particular configurations shown.
Federal Republic of Germany Patent No. 113,084 shows the use of a so-called "flexural spring" as a stiffening element within a tubular support in order to prevent the tube from buckling, a technique which originates from the field of tube bending. This flexural spring is further provided with head plates at its ends so that the spring can be introduced into the tube and removed after the bending operation is completed, and a chain or cable which is turnably fastened to one head plate is also provided.